There is an ever-increasing growth of wireless communication and the development within this field entails making all kinds of portable devices as small as possible in order to render them more convenient to bring along anywhere. The development towards smaller and smaller portable devices is obviously accompanied by requirements for smaller building blocks or electronic components comprised within the devices, posing several challenges to the engineers designing the components. The progresses in making devices and circuits smaller bring about costly development work, and as the manufacturers compete in offering the users the smallest possible mobile equipment most worth its price, production costs of portable devices are a concern to them.
The more components that are required the higher the chip count and cost of implementing the circuit as well as increased complexity in wiring. Simplifying the wiring of a circuit often reduces the overall costs considerably, as does any reduction of the number of components. Further, eliminating components also decreases the power being dissipated by the circuit, requires less cooling and entails lessened power consumption.
Portable devices such as mobile phones require a multitude of electronic components, for example RF (Radio Frequency) modulators comprising, among other things, voltage controlled oscillators, mixers and power amplifiers. All these components naturally require current and each component also adds to the complexity and wiring and therefore cost of the mobile phone.
Examples of state of the art RF modulators are direct Voltage Controlled Oscillator (VCO) modulators and complex In-phase and Quadrature (I/Q) modulators. Direct VCO modulation is suitable only for Frequency Modulation (FM) and Frequency Shift Keying (FSK), while I/Q modulation is able to support any modulation scheme. I/Q modulation requires two mixers for receiving input signals I(t) and Q(t) carrying the information to be transmitted, and received from a previous step including base band signal processing. FIG. 1 shows a conventional modulator utilising I/Q modulation. The modulator 1 comprises a quadrature oscillator 3 and input signals I(t), Q(t) are mixed with carrier signals cos(ωLOt),sin(ωLOt) in mixers 2a, 2b. The resulting mixed I(t) and Q(t) signals are added by an adder 4 resulting in a signal g(t).
Further, the modulated signal g(t) of the I/Q modulator has to be amplified before being output to the antenna, which amplification is performed by power amplifiers (PA) 5. The power consumption of a portable device is often of great concern, and a power amplification stage of such device consumes a large part of the power source capacity. Reducing the power consumption in the power amplification stage can entail a profound impact on overall device battery life.
It would thus be desirable to be able to simplify the design of an RF modulator further yet, reducing its size and weight and lowering the power consumption.